Among other things, the control of internal combustion engines requires knowledge of the pressure currently prevailing in the combustion chambers of the cylinders of the internal combustion engine.
What are understood as combustion-engine pressure sensors, which measure the pressure and convert it into an analog electrical voltage, are used for this purpose. This analog voltage value is then transmitted by way of corresponding lines to a control unit and evaluated by the control unit.
In most cases, such sensors operate on the basis of a linear correlation between the measured pressure and the generated analog voltage; as a result, the control unit is able to draw conclusions with regard to the pressure in the combustion chamber, e.g., expressed in the bar unit, on the basis of the received analog voltage.
Using the combustion-chamber pressure as an example, the resolution in volt per bar (V/bar) during the generation and transmission of the analog voltage is calculated with the aid of the predefined pressure range.
Given a pressure range of 200 bar in the combustion chamber and an effective total voltage swing for the sensor of maximally 4.5 V, a resolution of 22.5 mV per bar is obtained as a result.Voltage swing/pressure range=resolution (4.5 V/200 bar=22.5 mV/1 bar)
This means that small changes in the combustion-chamber pressure are reproduced by only a few mV and that heavy interference may therefore occur in this voltage value during the analog transmission on a transmission line to the control unit.
For example, such interference may be caused by adjacent electrical or electronic components such as drive motors, ignition components and others.
As a result, an evaluation of small changes in a parameter such as a pressure, a rotational frequency or other variables is made more difficult or impossible on account of the interference that is superposed on the useful signal.